1. Field of the Invention
This invention relates to the field of laminating plastic sheets or films, particularly polyvinyl chloride (PVC) films to produce credit cards, tiles, wall panels, and the like. The invention relates particularly to a method in which the final product includes at least one layer of rigid PVC.
Presently existing methods of producing laminated plastic for tiles, large panels, credit cards, printed circuits, engraving laminates and the like, require such equipment as high compression presses and involve the steps of heating and cooling the platens which may be 1-2" (2.54-5.08 cm.) thick. These processes are expensive in terms of energy consumption and time involved due to the large mass that must be heated and cooled. A complete processing cycle of this type may take from forty minutes to an hour. Moreover, the process, which is inherently a batch-type process, frequently results in a final product that is subject to deformation due to the stresses which remain after processing. To prevent deformation, tiles, for example, are secondarily annealed in an oven at 71.degree. C.-82.degree. C. (160.degree. F.-180.degree. F.) for at least one and a quarter hours and allowed to cool slowly and naturally. Nevertheless, some of the tiles still contain stress which is difficult, if not impossible, to remove entirely.
2. The Prior Art
U.S. Pat. No. 3,383,265 discloses a process for welding together two plastic sheets in a chamber having at least one flexible diaphragm. In this process, heat is applied with an infrared or other heat source while the flexible diaphragm is pressed against the joint until it melts into the weld. U.S. Pat. No. 4,104,101 discloses the use of heat and at least one flexible diaphragm to form plastic powder into a sheet or film. That patent also discloses that it is possible to make a high bond strength laminated product from two layers of the same or different powdered plastic material. Neither of these patents discloses how pre-existing plastic films may be laminated, especially in large widths.